Equating ants ability to percieve sound with the hearing of humans is not realistic. However, it's thought that ants do percieve sound in two ways; feeling vibrations through their contact with the ground and, at least in the very close distances, they appear to be able to recieve sounds through small hair like structures on their antennae...
cidermonkey I don't know the answer to your question but I am laughing my head off imagining someone sneaking up on an ant and shouting at them. Saying that if someone did it where I live it wouldn't be considered wierd as everyone round here is crazy. Thinking about it I think ants must have pretty good hearing cos I've never seen one wearing an hearing aid.